CS10
The Beauty and Joy of
Computing
Lecture #25 : Tree Recursion
UC Berkeley
EECS
Lecturer SOE
Dan Garcia
2010-11-29
MS KINECT = BODY
I/O
The newly released (and muchhyped) Microsoft Kinect system
for the XBOX 360 used
controller-free body motions to
control games, music, and
movies.
xbox.com/kinect/
Review: What’s in a Strong Solution
 For every position
 Assuming alternating play
 Value …
(for player whose turn it is)
Winning ( losing child)
Losing (All children winning)
Tieing (! losing child, but 
tieing child)
Drawing (can’t force a win
or be forced to lose)
 Remoteness
 How long before game
ends?
W
L
...
WWW
...
L
WWW
T
D
...
WWW
W
D
...
T
WWW
W
Garcia, Fall 2010
UC Berkeley CS10 “The Beauty and Joy of Computing” : Tree Recursion (2)
Review : Example: 1,2,…,10
 Rules (on your turn):

Running total = 0
 Rules (on your turn):

Add 1 or 2 to running total
 Goal

Be the FIRST to get to 10
 Example
 Ana: “2 to make it 2”
 Bob: “1 to make it 3”
 Ana: “2 to make it 5”
 Bob: “2 to make it 7” 
7 ducks (out of 10)
photo
 Ana: “1 to make it 8”
 Bob: “2 to make it 10” I WIN!
Garcia, Fall 2010
UC Berkeley CS10 “The Beauty and Joy of Computing” : Tree Recursion (3)
Let’s write code to determine value!
 0 = Win
 P = Position
 1 = Lose
 M = Move
 2 = Win
 We only need 3 blocks to define a
game
 3 = Win
 4 = Lose
 5 = Win
 6 = Win
 7 = Lose
 Do Move M on Position P
  a new Position
 Generate Moves from Position P
  list of Moves
 8 = Win
 Primitive Value of Position P
 9 = Win
  {win, lose, tie, undecided}
 10 = Lose
 Let’s write Value of Position P
Garcia, Fall 2010
UC Berkeley CS10 “The Beauty and Joy of Computing” : Tree Recursion (4)
Answer
Garcia, Fall 2010
UC Berkeley CS10 “The Beauty and Joy of Computing” : Tree Recursion (5)